Industrial waste water as well water-borne waste and paints derived from industrial processes such as electrophoretic and spray-booth painting can cause serious pollution problems. Water-born paints, and waste water when discharged as aqueous carrier with paint or lacquer residues, increase substantially the chemical oxygen demand (COD). Such paint and lacquer deteriorate by ageing or chemical modification, become sticky or hard, resulting in pipe and equipment blockage which are extremely difficult to clear.
In addition to the prior art disclosed in U.S. patent application Ser. No. 842,515, filed on Mar. 21, 1986, the following prior art patents are related to the subject matter of this application:
U.S. Pat. No. 4,067,806 of Frank A. Mauceri, discloses a process of detackification of paint and spray booth lacquer by using amphoteric salts (like zinc chloride etc.) and a terpolymer-"graft"-on diallyldimethylammonium halide, N-vinylpyrrolidone and acrylamide. The compositions have tremendous disadvantage by using amphoteric salts like ZnCl.sub.2, which will form zinc hydroxide only at high pH of 10 to 10.5. Below and above this pH range, the zinc hydroxide is soluble again, so the floc forms. On the other hand, the zinc hydroxide is very fluffy and unstable, and absorbs much water which makes the products very unsecure in this kind of application. The waste water and the sludges are alkaline and can not be discharged without further treatment, which makes such processes uneconomical. Further, under the conditions described in the patent, the amphoteric salt (ZnCl.sub.2) can easily be transformed into inactive anion like (ZnCl.sub.3).sup.- by the reaction: ##STR2## which decreases the efficiency to treat and/or kill the anodic and/or cathodic paints, lacquer, etc.
U.S. Pat. No. 3,990,986 of Gabel, et al, like Mauceri, teaches detackification of the paint and lacquer by using amphoteric salts (like ZnCl.sub.2) or a blend with alkanolamines and/or aliphatic amino alcohols. This patent presents the same negative aspects as Mauceri. Note also that the test conditions of detackification use an insufficient amount of paint (0.5 cc/500 mls of water) for a fair test. The product selected, such as polyalkylene oxide with molecular weight (Mw) of 200 has low Tg (glass transition temperature) which makes the reaction hydrophilic, resulting in very unsecure floc, and the paint may be only partially killed.
U.S. Pat. No. 4,401,574 of Farrington, et al, uses polyaluminum chloride (PAC) in paint waste water, such as polyvinylacetate latex based paint or vinyl-acrylic paint. The (PAC) alone or mixed with regular aluminum and/or iron salts (chloride, sulfate) are totally ineffective on air-borne paint and lacquer waste water treatment. Even in regular paint waste water, the water clarity (35 NTU) is still hazy.
U.S. Pat. No. 4,182,839 of Tesson discloses the process of manufacturing cationic resin soluble in water, based on melamine formaldehyde-alkyl and/or alkanolamine-hydrochloric acid. The products are used in the paper industry, to develop resistance of paper to humid conditions.
U.S. Pat. No. 4,504,396 of Harpel, et al. discloses compositions based on a hectorite clay, an antifoaming agent, aluminum oxide and montmorillonite clay as a paint detackifier agent.
Electrophoretic paints consist of an organic substrate on which ionic charges have been introduced. Today's market can offer anodic electropaints or a cathodic formulation. For more than twenty years, the method of treatment has been to add a chemical coagulant (either ferric or aluminum salts) in a controlled pH environment to form a hydrous oxide floc onto which that paint can be adsorbed. The anodic paints become sticky if they encounter acid conditions and cathodic paints become sticky in alkaline conditions. Application of solvent-based paints by spraying, followed by a hardening stage is extensively practiced for motor car body finishes over the electropaint primer. The spraying is carried out in a booth with exhaust system to extract surplus air-borne paints. Any removed material passes through a curtain of recirculating water, which will absorb paint and solvent, and which has to be removed before the waste water is recirculated.
The most common paints used are classified into two groups:
a. Spray-booth paints such as thermosetting acrylic clearcoat, thermosetting acrylic enamel, thermoplastic acrylic lacquer and stoving alkyd.
b. Electophoretic paints such as acrylic based anodic, epoxy-based cathodic and polybutadiene based anodic.
Other paint-varnish systems which may be used are:
1. Epoxy, such as pre-polymerized epoxy resin, amide-epoxy (crosslinked copolymers).
2. Styrenated alkyd
3. Drying oils
4. Phenolic resin
5. Urea alkyd
7. Urea melamine
7. Silicone
The treatment system commonly used is controlled additions of coagulants with simultaneous pH control which are removed by air flotation, electroflotation or sedimentation, slurryholding and filter press. In the case of air flotation, full chemical coagulant with good performance is still to be achieved. the regular ferric or aluminum sulfate, though largely unsuccessful for coagulation processes, are used as paint "killer". The industrial waste water and water-borne paints treated with the inorganic-organic and/or organic alloy polymer adducts have a high impact on coagulation processes. These act as primary coagulants which under neutralization processes (preferable "hydrophobe" compositions) will floc and kill the paint. Good performance was produced with an operating pH of 6.0 to 9.0 for anodic and cathodic paint which gives high supernatant clarity and high settling and/or dewatering rates. As pH can be used any reagents, or alkaline inorganic and/or organic matter but preferable are the hydrophobe alkaline agents. For the preparation of "hydrophobe" alkaline material, the following can be used:
a. Any inorganic and/or organic alkaline matter such as NaOH, KOH, Ca(OH) , sodium aluminate, potassium aluminate, sodium zincate, sodium silicate and/or metasilicate, sodium borate, alkyl amines, alkanol amines or mixture of these in combination with "hydrophobe" materials.
b. (Co)polymers, surfactants (preferably nonionics and/or anionics and/or mixture of these from 0.5%b.w. - 95.5%b.w. -0.5%b.w.). The most preferable hydrophobe products are the (co) polymers such as cationic polyamine, or vinyl latex type as ethylenicaly, styrene latex, styrene-divinylbenzene latex, styrene butadiene (modified) latex, styrene acrylates or acrylic latex, acrylates or natural polymers type.
c. Hydroxy alkyl(poly)carboxylate salts or acids such as sodium gluconate, sodium gluco heptonate, modified natural (co)polymers salts, sodium rosinates, sodium glucosides or other cation combinations, clay and bentonite modified inorganic or organic type including cationic types.
d. Other products used can be in any forms as inorganic/or organic alkaline stripper agents including halogenated types and/or in combination with products (a), (b) and/or (c).
For air and/or electroflotation, NaOH is the most commonly used, producing as well as hydrophobe agents in some cases, less dense and easily floated flocs. For anodic paint treatment, alkali dosage can be used before the coagulation addition, therefore the final pH is approached from the high pH end.
Polyelectrolyte selection is very important too. These must have very high molecular weight (Mw). In the case of waterborne paint waste water, a dosage of less than 1.0 ppm often improved supernatant clarity and fast settlement. Higher concentrations may tend to produce bulky, open-textured flocs.